OCEANIC CRUSTAL THICKNESS VERSUS SPREADING RATE

A compilation of oceanic crustal thickness from seismic observations collected over the past two decades shows that the average crustal thickness, away from plateaus, is 6 km; no systematic increase of crustal thickness with spreading rate is observed. Instead, the data show large variations in crustal thickness at slow spreading ridges (3 - 8 km for half rates < 20 mm/yr) and small variations in thickness at fast rates (5 - 7 km for half rates > 30 mm/yr). The large variations at slow ridges and small variations at fast ridges are consistent with the results inferred from recent gravity studies of mid-ocean ridges. Both data sets support the speculation of a transition from a 3-D structure of crustal accretion at slow ridges to a 2-D accretion pattern at fast ridges.